Hitherto used and known rail vehicle slack adjusters of the axial type have barrels in principal consisting of a metal tube and end pieces machined to the desired shape and assembled. In order to obtain the desired functions at the end pieces and the required strength and stability for the barrel as a whole the barrel will be thick and heavy and the machining cost considerable, all adding to great weight and high price. Besides, the mounting of the different parts of the adjuster may sometimes be difficult due to the tube-shaped barrel.